1. Field of the Invention
The present invention relates to an anisotropic conductive film capable of electrically and mechanically connecting an electronic part (e.g. IC chip, and a liquid crystal display (LCD) panel in a liquid crystal display (LCD)) and a substrate, or connecting substrates, and also relates to a joined structure using the anisotropic conductive film.
Moreover, the present invention also relates to a method for producing an isotropic conductive film (a film containing aligned particles) in which conductive particles aligned into a monolayer at a pitch of micron-order in a resin film.
2. Description of the Related Art
Anisotropic conductive films (ACF) have conventionally been used as means for connecting electronic parts and a circuit board, and the like. The anisotropic conductive film is used for adhering and electrically connecting various terminals to each other, including the case for connecting a flexible print circuit or terminals of IC chip to an indium tin oxide (ITO) electrode formed on a glass substrate of a LCD panel.
As for the anisotropic conductive film, the film in which conductive particles are dispersed in an epoxy resin-based insulating adhesive layer is generally used. For example, the electrical connection between the terminal of the IC chip and the ITO electrode is realized by holding and crushing the conductive particles between the terminal of the IC chip and the ITO electrode of the glass substrate.
The area of the contact terminal is reduced as the contact terminals are arranged at finer pitch due to the recent trends of the electronic devices, such as downsizing and having higher performance. Although the area of the terminal is reduced, it is still desired to maintain the high conduction reliability.
Since the conductive particles are dispersed in the insulating adhesive layer, the anisotropic conductive film has a problem such that the conductive particles are moved along with the movement of the insulating adhesive agent by heating and contact bonding at the time of the connection. To make the electrical connection secure, it is necessary to make the number of the conductive particles on the terminal at a certain level or larger after the connection. Therefore, it is also necessary to increase the number of the conductive particles to be contained in the insulating adhesive layer.
To this end, it has been desired to develop an anisotropic conductive film which suppresses the movement of the conductive particles, increases the capturing rate of the conductive particles at the terminal, and improves the conduction reliability, by regularly aligning the conductive particles on one plane of the insulating adhesive layer in the thickness direction.
For example, the following methods have been known as the method for producing an anisotropic conductive film in which the conductive particles are regularly aligned (the method for aligning the conductive particles on the electrode terminal or wiring for the purpose of the production of the anisotropic conductive film).
Japanese Patent Application Laid-Open (JP-A) No. 2006-32335 discloses an anisotropic conductive film in which conductive particles are disposed at a surface of an insulating adhesive layer, and proposes, as a method for evenly disposing the conductive particles in a surface layer of the insulating adhesive layer, a system such that the conductive particles are charged so as to have an identical electric charge, and are sprayed. In this system, however, the charge of the conductive particles can be lost within only several tens seconds, it is difficult to maintain the aligned state of the conductive particles on the insulating adhesive layer.
Moreover, JP-A 2002-75580 discloses a method for producing an anisotropic conductive film in which conductive particles are disposed only in a certain region, and proposes, as a method for disposing the conductive particles only in the certain region, a method in which a voltage is applied to the conductive particles, and the conductive particles are splayed at the region of the adhesive layer corresponding to the electrode by means of a mask which has an opening at the region corresponding to the electrode on the substrate. In this method, however, the electric charge of the conductive particles are diffused as the thickness of the adhesive layer is increased, and thus the fine alignment of the particles corresponding to the electrode cannot be attained.
Moreover, JP-A No. 2007-115560 discloses an anisotropic conductive film in which conductive particles are regularly aligned, and the production method thereof. This patent literature also proposes, as a method for regularly aligning the conductive particles, a method in which after spraying and aligning the conductive particles on a surface of an insulating adhesive layer which has been formed by applying the insulating adhesive on a substrate, an insulating adhesive is further applied thereon, or spraying the dispersion in which the conductive particles are dispersed in the insulating adhesive. In this method, however, the conductive particles are aggregated to each other if the pitch of the alignment of the conductive particles is reduced. Therefore, it is difficult to align the conductive particles into a monolayer.
Moreover, other than the methods mentioned above, for example, JP-A No. 2006.93020 discloses a method for producing an anisotropic conductive sheet and proposes a method for aligning the conductive particles by a magnet, using conductive magnetic particles as the conductive particles. In this method, however, the currently commercially available conductive particles cannot be used, and there is a problem in versatility.
Accordingly, it is a current situation that a simple method, which can align conductive particles into a monolayer in an insulating resin film at a pitch of micro order without causing the aggregation of the conductive particles, and align the conductive particles on one plane of the insulating resin film in the thickness direction thereof, has not been yet provided. There has been desired an anisotropic conductive film, which has excellent conduction reliability by suppressing the movement of conductive particles at the time of the connection between electronic part or the like and a substrate, and securing the high capturing rate of conductive particles, and developments of the relevant technique thereof.